NASA Learns More About Interstellar Visitor 'Oumuamua

An artist's concept of interstellar asteroid 1I/2017 U1 ('Oumuamua) as it passed through the solar system after its discovery in October 2017. Observations of 'Oumuamua indicate that it must be very elongated because of its dramatic variations in brightness as it tumbled through space. Credit: European Southern Observatory / M. Kornmesser

In November 2017, scientists pointed NASA's Spitzer Space Telescope toward the object known as 'Oumuamua—the first known interstellar object to visit our solar system. The infrared Spitzer was one of many telescopes pointed at 'Oumuamua in the weeks after its discovery that October.

'Oumuamua was too faint for Spitzer to detect when it looked more than two months after the object's closest aproach to Earth in early September. However, the "non-detection" puts a new limit on how large the strange object can be. The results are reported in a new study published today in the Astronomical Journal and coauthored by scientists at NASA's Jet Propulsion Laboratory in Pasadena, California.

The new size limit is consistent with the findings of a research paper published earlier this year, which suggested that outgassing was responsible for the slight changes in 'Oumuamua's speed and direction as it was tracked last year: The authors of that paper conclude the expelled gas acted like a small thruster gently pushing the object. That determination was dependent on 'Oumuamua being relatively smaller than typical solar system comets. (The conclusion that 'Oumuamua experienced outgassing suggested that it was composed of frozen gases, similar to a comet.)

"'Oumuamua has been full of surprises from day one, so we were eager to see what Spitzer might show," said David Trilling, lead author on the new study and a professor of astronomy at Northern Arizona University. "The fact that 'Oumuamua was too small for Spitzer to detect is actually a very valuable result."

'Oumuamua was first detected by the University of Hawaii's Pan-STARRS 1 telescope on Haleakala, Hawaii (the object's name is a Hawaiian word meaning "visitor from afar arriving first"), in October 2017 while the telescope was surveying for near-Earth asteroids.

Subsequent detailed observations conducted by multiple ground-based telescopes and NASA's Hubble Space Telescope detected the sunlight reflected off 'Oumuamua's surface. Large variations in the object's brightness suggested that 'Oumuamua is highly elongated and probably less than half a mile (2,600 feet, or 800 meters) in its longest dimension.

But Spitzer tracks asteroids and comets using the infrared energy, or heat, that they radiate, which can provide more specific information about an object's size than optical observations of reflected sunlight alone would.

Scientists have concluded that vents on the surface of 'Oumuamua must have emitted jets of gases, giving the object a slight boost in speed, which researchers detected by measuring the position of the object as it passed by Earth in 2017. Credit: NASA/JPL-Caltech

The fact that 'Oumuamua was too faint for Spitzer to detect sets a limit on the object's total surface area. However, since the non-detection can't be used to infer shape, the size limits are presented as what 'Oumuamua's diameter would be if it were spherical. Using three separate models that make slightly different assumptions about the object's composition, Spitzer's non-detection limited 'Oumuamua's "spherical diameter" to 1,440 feet (440 meters), 460 feet (140 meters) or perhaps as little as 320 feet (100 meters). The wide range of results stems from the assumptions about 'Oumuamua's composition, which influences how visible (or faint) it would appear to Spitzer were it a particular size.

Small but Reflective

The new study also suggests that 'Oumuamua may be up to 10 times more reflective than the comets that reside in our solar system—a surprising result, according to the paper's authors. Because infrared light is largely heat radiation produced by "warm" objects, it can be used to determine the temperature of a comet or asteroid; in turn, this can be used to determine the reflectivity of the object's surface—what scientists call albedo. Just as a dark T-shirt in sunlight heats up more quickly than a light one, an object with low reflectivity retains more heat than an object with high reflectivity. So a lower temperature means a higher albedo.

A comet's albedo can change throughout its lifetime. When it passes close to the Sun, a comet's ice warms and turns directly into a gas, sweeping dust and dirt off the comet's surface and revealing more reflective ice.

'Oumuamua had been traveling through interstellar space for millions of years, far from any star that could refresh its surface. But it may have had its surface refreshed through such "outgassing" when it made an extremely close approach to our Sun, a little more than five weeks before it was discovered. In addition to sweeping away dust and dirt, some of the released gas may have covered the surface of 'Oumuamua with a reflective coat of ice and snow—a phenomenon that's also been observed in comets in our solar system.

'Oumuamua is on its way out of our solar system—almost as far from the Sun as Saturn's orbit—and is well beyond the reach of any existing telescopes.

"Usually, if we get a measurement from a comet that's kind of weird, we go back and measure it again until we understand what we're seeing," said Davide Farnocchia, of the Center for Near Earth Object Studies (CNEOS) at JPL and a coauthor on both papers. "But this one is gone forever; we probably know as much about it as we're ever going to know."

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Maybe we should consider Oumuamua to be a reminder that chemical propulsion in space is extremely limiting. We need strong nuclear propulsion not just for fast, crewed missions to Mars, but also for giving us the flexibility we need to really explore the solar system and take advantage of opportunities out of reach with chemical propulsion.

Any idiot can use a calculator to divide one number by another, and quote all the numbers after the decimal place as if they were somehow significant.

In this case, anything after the first or second (take your pick) decimal place in your quoted number is meaningless fluff, since you haven't factored in uncertainties in the users' speed, or in the earth-moon distance.

In the first instance, the original specification was that the person take five years *or so* to walk around the earth (at the equator?), so there's a good degree of uncertainty right there in the walking speed.

Secondly, the moon's orbit is an ellipse, with eccentricity 0.0549, so there's more uncertainty.

The best one could say in this circumstance is what @wg said - roughly 50 years. Your quoted figure is meaningless, and you should learn the difference between apparent and real degrees of accuracy.

We have seen, close up & personal, that the surface of an asteroid can be swept clean of dust bunnies and peagravel. I think the cause is my "Carpet Beater Scenario". Another random rock bumps just hard enough to make the small crap jump far enough to escape the big rocks micro-gravity.

The speculation that Oumuamua is a comet? Now claims that the interstellar hermes did not outgas because the surface is frozen solid? That kinda spoils the fantasy that there were jets "steering" megatonnage of solid rock. Without being observed. "Okay, now pull the other one!"

I'm still waiting for someone to do the math of how much the delta/v budget, the mass of reaction matter, would have to be to steer a megaton of rock.

- cont'd -Especially when Oumuamua was coursing away from the Sun. All that energy applied from Solar radiation? And no visible coma?

So, on that evidence, no ice. Just a solid chunk of core nickel-iron. Which traveled too quickly by the Sun to have time to heat up.

Which explains why Oumuamua is not visible om infra-red. And uncertainty of it's present course due to unpredictable gravitational tug from the planets.

Yes Mark, we should have nuclear powered, robotic manned, deep space craft for such missions. With a picket englobement of Early Warning Satellites. One set around the Earth/Luna and another around the Solar System.

However, all that is dependent on making the International effort to build an infrastructure of orbiting automated factories. Once past the cost of launching the original Mother factories? It should be mostly self-sustaining accessing space resources. Except for specialized equipment and technical upgrades from Earth.

Seems the evidence converges. The interesting thing is to see the next one - if they pass once every year and we now have telescopes covering that size range it should not take long to understand the distribution.

1: Is it possible the UFO's rotation was orthogonal to the direction of motion?

? It was an IFO, a likely comet. IIRC it was seen tumbling chaotically, which seems typical for non-spherical objects in space.

2: Is this the type of mechanics you would use to generate an artificial gravity?

It is the classical rotational mechanics that every natural non-spherical object obey. Of course, as a jetting comet it seems to have gotten a gas assist that imposed more or less rotational (and translational) momentum every now and then. Newton 101.

I still keep thinking about what would it take to run it down and catch Oumuamua . . .

Perhaps a series of flybys in the inner solar system could get a probe up to speed? I am not sure whether some combination of Earth and Venus flybys could impart enough velocity along a similar trajectory for a probe to catch up, but it would have to be a very cleverly crafted trajectory, if it could be done at all.

The best one could say in this circumstance is what @wg said - roughly 50 years. Your quoted figure is meaningless, and you should learn the difference between apparent and real degrees of accuracy.

1: But it takes an even greater idiot to fail to realize my calculation is arrived at using the average of the max and min distances divided by the earth's circumference. So no, 50 years is not a better number.2: Many idiots begin their flawed arguments with "Any idiot". They do this as an emotional appeal because the use of logic is a concept they will never understand.3: I am sure you have mastered the use of a calculator. They have actually invented something called the computer. This is what I used, along with a program named Octave. I have also used Octave to process signal data from the Allen Telescope Array and generate 3D surface plots. So my usage here was trivial. One point for you.

"The new study also suggests that 'Oumuamua may be up to 10 times more reflective than the comets that reside in our solar system—a surprising result,

Read more at: https://phys.org/...#jCp"The new study also suggests that 'Oumuamua may be up to 10 times more reflective than the comets that reside in our solar system—a surprising result,

Betcha polished chrome-moly would 'reflect' a LOT. Something a quarter mile long would take 'significant' thruster force to revector it. Changes in reflectivity could also imply a 'delta winged' or other morphology that rotated along its principle Veloc vector resultant as it 'faced' its cameras and antenna arrays toward Earth and Ceres and other undiscovered to us outposts.

WE better WAKE UP. We may not have as much time as we think to organize as a unified planet, get hold of our environment, and pr

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